Studies of the mechanism of interaction of bovine neurophysins with oxytocin, vasopressin and small peptide analogs of the hormones will be continued. Specific projects include: 1) Determination of the entropic and enthalpic contributions of individual segments of the hormones to their free energy of interaction; 2) Measurement of the distance between the single neurophysin tyrosine and the binding site by NMR studies using nitroxide-spin-labeled analogs of the hormones; and 3) Chemical modification studies aimed at elucidating the role of the internally duplicated neurophysin sequences in the binding of hormone. Additionally, work in progress on the crystallization of neurophysin-peptide complexes will continue. BIBLIOGRAPHIC REFERENCES: North, W.G., Walter, R., Schlesinger, D.H., Breslow, E. and Capra, J.D, "Structural Studies of Bovine Neurophysin-1," Annals of the New York Academy of Sciences," 248, 408-422 (1975). Breslow, E., "Hormone-Neurophysin Binding: A Model for Peptide-Protein Interaction," Annals of the New York Academy of Sciences," 248, 423-441, (1975).